During operation of nuclear reactors, debris builds up in the system piping, tanks, heat exchangers and such (hereinafter “the system”). This build up can include sludge, scale, deposits and corrosion products or other metallic species. These deposits may or may not be contaminated with radioisotopes. These deposits are harmful to the system's components or tanks and must be removed. There are numerous chemical processes that may be applied for the removal of the material build up. These chemical processes vary in chemical formulation, application methodology and efficiency. The current state of the art chemical processes utilized for the dissolution and mobilization of the corrosion products and sludge build up produces large waste volumes which are difficult to treat and ultimately to dispose of. Typically the waste material is a liquid, however, it may be condensed into a very concentrated liquid that needs to be maintained at higher temperatures in order to remain in a liquid state. The large volumes of liquid waste require treatment prior to disposal and must be transported to the disposal site. The liquid wastes typically contain chelating agents and/or organics that require stabilization in order to meet State and/or U.S. Federal disposal guidelines, increasing the disposal difficultly and expense. Generation of these large volumes of liquid waste typically requires an environmental permit to be filed with States Regulatory Agencies.
There are several processes that utilize chemicals to remove sludge, deposits, scale, corrosion products or other complexed metal ions. Corrosion product removal processes include Chemical Oxidation Reduction Decontamination (CORD); Low Oxidation State Metal Ions (LOMI); and CAN-DEREM. Scale or deposit removal process typically contains EDTA (ethylenediamine tetraacetic acid). Scale or deposit removal processes include EDTA based steam generator cleaning proprietary solutions such as EPRI SGOG and Advanced Scale Conditioning Agents (ASCA). Each of these processes requires a specific application temperature to efficiently remove the sludge materials and generates process specific liquid wastes which are difficult to stabilize and expensive to handle.
As discussed above, a problem with the current corrosion product chemical dissolution processes is that they generate large quantities of chemical liquid waste, which is difficult to dispose of due primarily to the presence of the chelating agent such as EDTA. Typically, multiple chemicals are mixed into these chemical chelating solutions. Current processes require significantly longer application times at narrow band specific temperatures in order to dissolve or mobilize the sludge, corrosion products, and other materials discussed.
The necessary narrow band specific temperatures required by conventional chemical processes need more equipment on site and may involve recirculation of the system to be cleaned with a reactor cooling pump or other mixing device in order to maintain the optimum temperature. The use of multiple chemicals required to optimize the process dissolution or mobilization technology results in additional expense and/or time to either mix the chemicals at an off-site location or the need for sufficient tanks on site to mix the chemicals.
The conventional processes also require 24 hours or longer for dissolving, mobilizing or otherwise treating the sludge, scale, corrosion product or deposits. The longer the system is exposed to the chemical process, the higher the chance for additional corrosion or other challenges that might occur during the process.